Bell less top charging installations have found widespread use in blast furnaces around the world. They commonly comprise a rotary distribution device equipped with a distribution chute which is rotatable about the vertical central axis of the furnace and pivotable about a horizontal axis perpendicular to the central axis. In multiple hopper installations, two or more material hoppers are arranged in parallel; each provided with their own inlet and outlet gates. While material is fed from one hopper into the metallurgical furnace, another hopper can be simultaneously filled with material. In order to ensure that the correct amount of material is fed into the metallurgical furnace, each material hopper comprises a weighing system for determining the weight of the material hopper and its content. Such weighing systems require a relative movement between the material hopper and the metallurgical furnace. Bellow arrangements, which are also often referred to as compensators, are generally used to compensate for such relative movement. While reference is here made to the use of bellow arrangements in connection with a charging installation of the parallel hopper type, the same are used in other types of charging installations, such as e.g. the central feed type. Also, bellow arrangements can be arranged in ducts, such as e.g. pressure relief duct.
Such compensators form a pipe with a bellow section formed by a series of folds which provide some flexibility between the inlet and outlet ends of the pipe. The folds form pockets, which are required for achieving this flexibility. The inner pockets of the bellow section are exposed to the material passing through the pipe. Any material or dust accumulation in these pockets reduces their size and thus the flexibility of the bellow section. Eventually, once sufficient material or dust has accumulated in the pockets, the bellow section is said to be clogged and is no longer able to fulfill its full function. Clogged compensators prevent the weighing system from working correctly as the relative movement between material hopper and metallurgical furnace is no longer guaranteed. Correct determination of amount of material fed into the metallurgical furnace is however essential for the correct functioning of the latter. Thus, it is important to prevent clogging of the compensators.
It has in the past been suggested to arrange a protection plate inside the compensator for directing material past the pockets. Such a protection plate may e.g. be welded to the inlet end of the pipe, i.e. above the bellow section, and run past the bellow section to a region below the bellow section. In order to allow relative movement between the inlet and outlet ends of the pipe, the protection plate cannot be welded to the outlet end of the pipe. Such a protection plate allows for material to be guided past the bellow section and reduces material accumulation in the pockets. Furthermore, an annular gasket may be arranged at the outlet end of the pipe between the protection plate and the pipe. Due to the annular gasket having to cope with relative movement between the protection plate and the pipe and due to the high pressures reigning in the pipe, such a gasket cannot completely prevent dust from penetrating into the region between the protection plate and the bellow section. Thus, dust can still accumulate in the pockets of the bellow section and, with time, prevent the correct functioning of the compensator.